There are systems in which a plurality of users exchange music data free of charge. In such a system, one user, who holds music data, may provide another user with the music data through the Internet, and then may receive different music data from another user.
If one content such as a piece of music is available in such a system, all users can theoretically enjoy that content. Many users may then stop purchasing the same content. The copyright holder misses the chance of receiving royalties for the use of the content even if the content is sold.
Society requires that an unauthorized use of any content be prevented without impeding the circulation of contents.
In known DRM (Digital Rights Management) systems for protecting the copyright of a content, one device has difficulty in importing a content from another device of a different format or a different method, and in exporting a content of its own to the other device.
When a content is imported or exported, a part of information of the content may be sometimes missing.
The other device has been unable to handle an imported or exported content in the same way as other contents are handled. In other words, the other device cannot handle the contents in a consistent manner.